The purpose of this study is to evaluate the long-term efficacy and safety profile of tosedostat in elderly patients suffering from refractory or relapsed Acute Myeloid Leukemia.

Extension protocol to the OPAL Study (CHR-2797-038).

Study mimics normal clinical practice; few procedures and visits are therefore mandated by the protocol. Timing of bone marrow assessment is also left at the investigator's discretion.

Inclusion Criteria:

• Signed, informed consent
• Completion of Visit 11 in the OPAL Study (Month 6 Visit)
• Investigator's opinion that the subject would benefit from continued therapy with tosedostat.

Exclusion Criteria:

• Any co-existing medical condition that in the Investigator's opinion will substantially increase the risk associated with the subject's participation in the study
• Psychiatric disorders or altered mental status precluding understanding of the informed consent process and/or completion of the necessary studies
• Administration of any (other) investigational agent within 14 days of entry into TOPAZ.